The irradiance profile of a laser is typically Gaussian, i.e., the beam intensity in a plane normal to the beam is highest at the center or beam waist point and decreases as the distance from the center point increases. Such a distribution is not desirable for applications where the beam is to be uniformly applied to an area. Such applications include: material processing, e.g., welding, soldering; biomedical applications, e.g., laser surgery; illumination applications, e.g., semiconductor mask fabrication, optical data processing, optical computing; and research requiring uniform beams.
The simplest technique for modifying the irradiance profile is attenuation, where the beam is truncated spatially using a filter or an aperture. This technique suffers the obvious disadvantage of removing energy from the beam.
The multifaceted integrator approach to laser beam shaping is especially suitable to laser beams with highly irregular (multimode) irradiance distributions. The number and size of the facets are selected to accomplish the required integration or, equivalently, averaging. However, actual production of the required multifaceted mirror is difficult and expensive.
For single mode beams with a Gaussian profile, previous solutions have attempted to map the beam into a uniform intensity profile with steep skirts. This mapping consists of various techniques for associating the phase element with the phase of desired irradiance profile. One set of techniques is a geometrical and iterative in nature. As such, this set does not effective model the system, resulting in suboptimum design. Remaining approaches require assumption of target distribution without any criteria for which distributions are physically allowable. Again, these solutions are not optimal. None of the techniques offers any suggestions for improving, or even assessing, system performance.